Amplifier



0%. 1'5, 1935. G, BEERS 2,017,523

AMPLIFIER Filed Jan. 26, 1952 2nd Dete cTor AUDIO 2 nd DetecTor AUDIDAAAAAA INVENTOR.

George L.Bee1"3,

J I I ,r s ATTORNEY.

Patented Oct. 15, 1935 UNlTED STATES PATN OFFICE AMPLIFIER of DelawareApplication January 26, 1932, Serial No. 588,909

41 Claims.

My invention relates to amplifiers and, more particularly, to amplifiersof the type suitable for use in the reception of radio signals.

In the design of radio receivers, there are two highly desirablecharacteristics that, in a sense, are mutually exclusive-that is, areceiver must be sufiiciently selective to differentiate betweenincoming signals under maximum and minimum sensitivity conditions and,at the same time,

1 high fidelity and freedom from distortion are desirable.

Heretofore, fair fidelity has been attained through the use ofinter-tube coupling circuits having bandpass characteristics. It hasbeen diflicult, however, to so design receivers, especially thoseprovided with automatic volume control, which will exhibit a high degreeof fidelity, as well as reasonable selectivity, when receiving signalsfrom local stations and still be sufficiently selective to receive weaksignals from distant stations without an unpleasant amount of backgroundnoise.

It is, accordingly, an object of my'invention to provide a radioreceiver wherein high fidelity is automatically had during the receptionof strong signals, without detriment-ally influencing the selectivity.

Another object of my invention is to provide, in a radio receiver, meansfor automatically increasing the selectivity during the reception ofweak signals.

Another object of my invention is to provide a volume control systemthat shall function satisiactorily without affectingv thecharacteristics of the amplifying tubes.

Another, and more specific, object of my invention is to provide a radioreceiver that, in addition to the features enumerated above, shall haveautomatic volume or gain control.

The foregoing objects, and other objects ancillary thereto, I prefer toaccomplish, in part, by supplying to the grids of certain of theelectronic tubes in a radio receiver grid-biasing po- 45 tentialscontrolled as to their amplitude by incoming signals. 1 also utilize theincoming signals to automatically control the damping in certain of theinter-tube coupling circuits and, concurrently therewith, the transferof energy to between the tubes.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and 55 its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of a specificembodiment, when read in connection with the accompanying drawing,wherein Fig. l

is a diagrammatic view of a portion of a radio 5 receiver embodying apreferred form of my invention, and Fig. 2 is a diagrammatic View of areceiver circuit embodying a modified form of my invention.

Although my invention is susceptible of appli- 1o.

quency amplifier tubes I, 3, 5, and I, and a detector tube 9. Each ofthese tubes may be of the screen grid, equi-potential, cathode typehaving an anode II, a screen grid I3, a control grid I5, anelectronically active cathode I1, and a heater I9. Preferably, however,the detector is of the three element type, as illustrated.

The several heaters, as is well known to those skilled in the art, maybe supplied with alternating current from any convenient low-potentialsource (not shown).

The first two tubes of the series are preferably connected through themedium of a radio frequency transformer 2!, the primary and secondarywindings of which are tuned and the coupling between them so adjustedthat the transformer efficiently passses a band of frequencies l0 KCabove and below the chosen intermediate frequency. The second and thirdintermediate frequency tubes are impedance coupled, the coupling networkincluding a tuned circuit 23 connected directly to the anode of thesecond tube and, through a coupling condenser 25, to the control grid ofthe next tube.

The third and fourth intermediate frequency amplifier tubes areconnected through a transformer 21 substantially the same as thatbetween the first and second tubes, and the last intermediate frequencytube and the detector tube are coupled through an equivalent transformer29.

A source of anode and grid biasing potentials (not shown) is supplied,across the output circuit of which is connected a resistor 3|. Platepotential for the second, third, and fourth intermediate frequencycoupling tubes is supplied over a connection 33 extending from theresistor, and the cathodes of these three tubes-also have a commonconnection 35 to a point on the resistor sufficiently more negativethanthe point to which the anodes are connected to provide the necessaryplate potential.

The detector is individually supplied with plate potential from theresistor, the primary winding of an output audio frequency transformer31 being included in the supply circuit. The detector is provided withself-biasing means which, preferably, takes the form of a resistor 39included between the cathode thereof and a point on the resistor.

The screen grids of the several intermediatefrequency amplifier tubesare, of course, provided with suitable positive potentials from theresistor, but the actual connections have been omitted from the drawingin order to simplify it.

If it is assumed, for the moment, that the first intermediate frequencyamplifier tube l is supplied with plate potential directly from theresistor, and with grid biasing potential also directly from the samesource, the system thus far described is of the type ordinarily found inthe majority of superheterodyne receivers. Obviously, such a systemresponds to every change in the amplitude of an incoming signal and isdevoid of means for automatically altering either the selectivity or thefidelity thereof in response to signal amplitude changes.

In order that automatic volume control may be had, it is necessarytoprovide some means whereby the increase in signal amplitude or, moreproperly, in the amplitude of the carrier frequency, may be met andcompensated by a change in gain. To this end, as disclosed in myapplication Serial No. 212,791, filed August 13, 1927, I provide avolume control tube 4| of the equi-potential type having an anode 43, acontrol grid 45, an electronically active cathode 41, and a heater 49.The grid of the volume control tube is variably connected through aresistor 5| to a point on the main potential supply resistor 3| morenegative than the point to which the cathode is connected and incomingsignals are applied thereto through a condenser 53 from the inputcircuit of the detector 9. I

The signal may, of course, be taken from any other point in the systemillustrated or from a point on a preceding stage (not shown).

The anode of the volume control tube is connected over a resistor 55 toa point on the main potential supply resistor 3| more positive than thepoint to which the cathode is connected and the said anode is alsoconnected to a conductor 5! common to the grid circuits of all theintermediate frequency amplifying tubes.

Preferably, the bias applied to the grid of the volume control tube isso chosen that the current flowing in the output resistor thereof duringnosignal intervals is only enough to maintain the grids of theintermediate frequency amplifier tubes sumciently negative to providemaximum sensitivity. However, as soon as an incoming signal makes itsappearance upon the grid of the volume control tube, the output currenttherefrom increases, with the result that the grids of the intermediatefrequency amplifier tubes acquire a more negative potential measured bythe potential drop acrossthe output resistor. The incoming signal,therefore, as it increases in amplitude, is met by reduced gain in thesystem, thus compensating for changes occasioned by fading and the like.

Since, as hereinbefore pointed out, a high de gree of fidelity isdesirable when receiving strong signals from local stations, some meansmust be supplied whereby the damping in' theinter-tube networks isincreased, or whereby the effective coupling between the primary andsecondary winding of an inter-tube transformer is automaticallytightened. To this end, I provide a plurality of thermionic devices 59and 6!, the only function of which is to alter the condition of thecoupling devices during the reception of strong signals from localstations. These devices are hereinafter referred to as the first andsecond fidelity-control tubes.

The fidelity control tubes may be of the equipotential cathode typehaving an anode 63, a control grid 65, a cathode 61, and a heater E59and the first tube is so disposed with respect to the output circuit ofthe second intermediate frequency amplifier tube 3 that the spacecurrent path therein is connected eifectively in shunt to the tunedoutput circuit 23 of the said tube. Plate potential for the firstfidelity control tube, accordingly, is supplied over the commonconductor 33 which supplies plate potential to the second, third, andfourth amplifying tubes.

The input circuit of the first fidelity control tube includes a resistorH which is serially connected between the output circuit of the firstintermediate frequency amplifying tube I and a point on the anode supplyresistor. The cathode of the tube may be connected to a point on theresistor slightly more positive than the point to which the inputresistor connects, in order that the tube may be biased normally to adesired point.

Since the space current path in the first fidelity control tube isconnected in shunt to the output circuit of the second intermediatefrequency amplifying tube, the impedance of this path controls thedamping in the said circuit, and also controls the energy transferbetween the second and third tubes. In order that the impedance may be afunction of the amplitude of an incoming signal, the previouslymentioned connection, including the resistor H, between the inputcircuit and the first intermediate frequency amplifier tube is made.

The connection of the cathode 61 to the resistor 3| may be provided withmanual adjustment to control the bias on the grid 65, if desirable. Ifthis is done, tone and selectivity control may be had at the will of theoperator.

The first fidelity control tube functions as follows:

Normally, as before explained, the grids of the intermediate frequencyamplifying tubes are supplied with just the right amount of negativepotential to maintain the said tubes in best condition for theamplification of weak signals. Such being the case, a definite amount ofspace current flows in each of the said tubes, the space current in thefirst tube, obviously, flowing through the input resistor l I of thefirst fidelity control tube. By proper choice of the magnitude of theresistor H, the drop in potential thereacross, when added to the biaspotential derived from the supply resistor 3!, the grid of the firstfidelity control tube may be so biased that the plate impedance of thetube is relatively high during no-signal intervals or during thereception of weak signals.

The selectivity of the system, therefore, insofar as the first andsecond tubes are concerned, normally is high, which is a desirablecondition for weak signal reception, to eliminate background noise, asalready pointed out.

7 However, as soon as the system is tuned to a strong signal, the platecurrent in the volume control tube 4| increases, as previouslyexplained.

with the result that the bias applied to the intermediate frequencyamplifying tubes becomes more negative, thus reducing the average platecurrent from the first intermediate frequency amplifying tube whichoccasions a decrease in the potential across the resistor II in theinput circuit of the first fidelity control tube.

The plate impedance of the last-named tube, therefore, decreases,permitting the tube to exert an increased shunting effect, at theintermediate frequency, upon the output circuit of the second IFA tube.The tuning of the output circuit, therefore, is broadened and thefidelity of reproduction increased while, at the same time, a decreasedamount of energy is transferred to the third IFA tube.

Since the decrease in energy transfer between he second and third tubesfurther reduces the gain in the system below the reduction occasioned bythe more negative grid bias supplied to the tubes from the volumecontrol tube, it may be desirable to provide further means whereby thedecrease in gain may, to some extent, be compensated without impairingthe fidelity of response of the system.

I, accordingly, provide the second fidelity control tube 6|, the spacecurrent path of which is effectively connected in shunt to the primarywinding of the transformer 2'! interposed between the third and fourthIFA tubes.

The transformer, as illustrated, comprises a tuned primary winding whichmay have a resistor 13 connected in shunt thereto and a tuned secondarywinding. The coupling between the said windings and the magnitude of theresistor are so chosen that the transformer passes a band of frequenciessufiiciently wide to give high fidelity.

The function of the second fidelity control tube is to decrease theeffective coupling between the primary and secondary transformerwindings during the reception of weak signals and to increase theeffective coupling during the reception of strong signals, with respectto the effective coupling during reception of signals of averagestrength. Obviously, the result is increased selectivity during weaksignal reception and increased fidelity during the reception of strongsignals.

In order that this function may be accomplished, the grid of the secondfidelity control tube is supplied with control potential directly fromthe plate circuit of the volume control tube 41, and the normal biasapplied to the grid of the said fidelity control tube is such that itoperates on the straight line portion of its characteristic curve. Suchbeing the case, the impedance of the tube is approximately 10,000 ohmsduring the no-signal state and, as the bias on the grid becomes more andmore negative in response to increased signal amplitude, the impedancerises to a higher and higher value thus effectively removing the shuntnormally established around the primary winding of the outputtransformer across which the space current path in the tube isconnected. The increased impedance of the tube, in response to increasedsignal amplitude, also increases the efiective coupling between thewindings of the transformer, thus broadening its characteristic curve atthe peak thereof and causing an increased energy transfer between thethird and fourth IFA tubes. It should, of course, be understood that theeifect of the second fidelity control tube, upon the selectivity andfidelity of response of the system, adds to the effect of the firstfidelity control tube.

In the event that it is desirable to reduce the expense of manufacturinga receiver according to my invention, some of the advantages thereof maystill be retained if the input circuit of the tube 59 is divorced fromthe plate supply lead 5 to the tube l and manually operable means areprovided for controlling the grid biasing potential ofthe said tube 59.Such means may take the form of a variable contact device associatedwith the main supply resistor 3| or any other 10 equivalent device.

Through variation of the grid potential of the tube 59, or gridpotential of a plurality of similar tubes, a continuous variation in theselectivity characteristic of the receiver may be obtained. 15

Under certain circumstances, it is desirable that volume control be hadwithout any change in the amplification characteristics of the severalthermionic devices, such as is caused by alteration of the grid or otherpotentials applied 20,

thereto. It, accordingly, lies within the scope of my invention todispense with grid potential control on the amplifier tubes and toprovide a system wherein certain of the tubes are either transformer orimpedance-coupled, as shown in 25. Fig. 1, and, further, to providemeans, instead, for altering the energy transfer between the severaltubes of the system in response to changes 7 in signal amplitude. Asystem so modified is shown in Figure 2 of the drawing.

Referring to Figure 2, a receiving system embodying a modified form ofmy invention com-- prises a plurality of intermediate frequencyamplifying tubes 15, 11, and I9 and a second detector tube 8|, each ofthe tubes, preferably, be- 35 ing of the screen grid, equi-potentialcathode type. The several tubes are inter-connected through couplingnetworks, each network comprising a tuned impedance 83 and a stoppingcondenser 85. 40

Further, each of the tubes may be provided with a self-biasing resistor81, if desirable, or the grids thereof may, instead, be connected toappropriate points on a main anode supply resistor 83. 1

The source of signals at the intermediate frequency is not shown in thedrawing, it being obvious that such signals may be derived from incomingradio signals in any customary and wellkno-wn manner.

Under normal conditions of no signal, or weak signal reception, it isdesirable that the system shall be extremely selective and that theenergy transfer between the successive tubes shall be a maximum. It is,further, desirable that, in the event the preceding stages of thecomplete system (not shown) be tuned to a strong signal, the overallgain in the system shall be reduced and the response characteristic bebroadened.

I have, accordingly, provided a plurality of gain-control tubes 89, 9!,and 93, the space current paths in which are, respectively, connected inshunt to the output circuits of the first, second, and thirdintermediate frequency amplifying tubes. I

In order that the gain-control tubes shall exert no shunting action uponthe tube circuits with which they are associated during the reception ofweak signals, it is necessary that their respective impedances bemaintained high. This, of course, may be accomplished by applying to thegrids thereof a potential of approximately the plate current cut-oifvalue.

It is also desirable that the impedances of the gain-control tubes shallbe reduced during the reception of strong signals, which reduction in 76impedance may be accomplished through automatic variation of the gridpotential applied thereto, in response to changes in signal amplitude.

I, accordingly, provide a master'gain-control tube having an inputcircuit constituted by a resistor 9i connected between the grid thereofand the main supply resistor 88 and an output circuit also constitutedby a resistor 99, the latter resistor, preferably, being shunted by acondenser NH. The cathode of the master selectivity control tube isconnected to a point on the anode supply resistor 88 sufficientlypositive with respect to the point of grid connection that the said tubeis biased to substantially the cut-off point.

It is, of course, to be understood that the normal bias on the tube 95may be varied to meet different requirements. In other words, if thegaincontrol tubes are not to function until an incoming signal hasreached a definite pre-determined value, the bias potential may be morenegative than the cut-off potential.

In any event, it is necessary that the master gain control tube shall sofunction as to rectify incoming signals in order that the current in theoutput resistor thereof shall be a function of the amplitude of the saidsignals. To this end, a connection 5533 including a condenser I extendsbetween the input circuit of the second detector tube 8i and the grid ofthe said master gain control tube whereby amplified incoming signals maybe impressed thereon. The connection I93 may, alternatively, be extendedto any other desired point in the system.

Obviously, from a consideration of the foregoin description, it will beapparent that increased signal strength results in an increasedpotential drop across the output resistor 99 which, if directly appliedto the grids of the gain control tubes, would increase their impedancesinstead of reduce them, as desired. Accordingly, since it is moreconvenient that the cathodes of the selectivity control tubes shall beconnected to the main supply resistor, as shown in the drawing, it isnecessary to interpose, between them.

and the master gain control tube, means whereby the phase of the voltageappearing across the output resistor of the last named tube may bechanged For this purpose, I prefer to utilize what might be termed aninversion tube ltl, the grid of which is directly connected to the plateof the master gain control tube and the output circuit of which includesa resistor Hi9 connected between the' anode thereof and the main supplyresistor. The junction between the anode of the inversion tube and theresistor is connected to a conductor Ill common to the grids of the gaincontrol tubes.

Accordingly, any change in potential across the output resistor 99 ofthe master gain control tube 95 is accompanied by a change in oppositesense across the resistor H39 in the output circuit of the inversiontube lill, and thegrids of the gain control tubes are thus given a morepositive potential in response to an increase in the amplitude of anincoming signal. The last named tubes, therefore, exert a shuntingaction upon the output circuits of the several intermediate frequencyamplifying tubes, the impedance of the gain control tubes decreasingwith increase in signal amplitude.

The shunting affect broadens the response of the system and, at the sametime, reduces the gain therein. A strong signal, therefore, is met bydecreased gain accompanied by improved fidelity,

those skilled in the art to which it pertains.

while a weak signal finds the amplifier highly selective and capable ofhigh amplification, the several enumerated functions being obtainedwithout any change in the grid biasing potentials applied to theamplifying tubes from the resistors 5 81, whereby their characteristicsremain unaltered. The advantages of my improved automatic volume,selectivity, and fidelity control system will be apparent, after acareful consideration of the foregoing description thereof. 10

Although I have selected certain embodiments of my invention for thepurpose of explanation, many modifications thereof will be apparent to yinvention, therefore, is not to be restricted except insofar as isnecessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a signal receiving system, a plurality of amplifying devices,coupling means inter-com necting said devices in cascade, means foralter ing the selectivity of the system through at least one of saidcoupling means in response to a change in the amplitude of a signalimpressed on said system and means connected with at least 25 one otherof said coupling means for compensating losses in gain caused byoperation of said second named means. i

2. In a signal receiving system, a plurality of amplifying devices,coupling means inter-connecting said devices in cascade, means foraltering the selectivity of the system through at least one of saidcoupling means in response to a change in the sensitivity of the systemand means connected with at least one other of said couplings 35 meansfor compensating losses in gain caused by operation of said second namedmeans, said selectivity altering means including a first fidelitycontrol device connected with said one of the coupling means forbroadening the tuning of and 4 decreasing the energy transfer throughsaid coupling means in response to increased average signal strength,and said gain compensating means including a second fidelity controldevice for increasing signal circuit coupling through said 45 other ofsaid coupling means in response to increased average signal strength.

3. In a signal receiving system, a plurality of amplifying devices,coupling means inter-connecting said devices in cascade, means forautomatically altering the gain of said system in response to a changeinthe amplitude of an incoming signal, means for altering the fidelitycharacteristic and energy transfer through at least one of said couplingmeans, and means for alter- 55 ing the effective circuit couplingthrough another of said coupling means, all in response to the change inthe average amplitude of an incoming signal.

4. In a signal receiving system, means for altering the gain therein inresponse to a change in the average amplitude of an incoming signal,means automatically responsive to the alteration in gain in effectivesignal circuit coupling in said system thereby to control the system forcontrolling the signal energy transfer therethrough and fidelitythereof, and a second fidelity control means responsive to changes inthe average amplitude of an incoming signal, said fidelity control meansbeing cooperative to increase the fidelity 70 characteristic of thesystem in response to increased average signal strength.

5. In combination, a plurality of electronic tubes connected in cascadethrough coupling devices to constitute an amplifier, means forimpressing signals on said tubes, means responsive to changes in averagesignal amplitude, for varying the fidelity and gain in opposite sensethrough one of said coupling devices, and means responsive to changes inaverage signal amplitude for varying the fidelity and gain in the samesense through another of said coupling devices.

6. The invention set forth in claim 5, wherein the effectiveness of thecoupling devices is altered through variation in the impedance of meansconnected in shunt relation thereto.

7. In a signal receiving system, means including a cascade connectedelectronic amplifier and a control circuit therefor for causing the gainin at least one of the amplifier coupling circuits to vary inversely andin another of the amplifier coupling circuits to vary directly with theamplitude of an incoming signal, said control circuit including meansfor causing the fidelity of response to vary inversely with the gain inone of said coupled circuits.

8. In a multi-stage amplifying system, means for causing the fidelity ofresponse to vary directly with the amplitude of an incoming signal andmeans whereby the gain in one of said stages varies inversely with thegain in another of said stages, simultaneously with the alteration inthe fidelity of response.

9. In a signal receiving system including a plurality of electronicamplifying devices, the combination of coupling means therefor arrangedto connect two of said devices in cascade relation, said coupling meansincluding two tuned coupled circuits, an electronic control deviceproviding variable impedance means connected in parallel with one ofsaid tuned circuits, and means for applying controlling potentials tosaid variable impedance means in a direction to cause the impedance toincrease when the signal strength is increased, thereby to control theselectivity characteristic of the system and the gain through saidcouplmg device in the opposite sense one with respect to the other.

10. A thermionic amplifying system including a plurality of cascadeconnected electronic amolifier devices, and means for controlling thefidelity and selectivity characteristic of the system in response tochanges in the average amplitude of signal currents transmittedtherethrough, said means including a pair of signal circuit couplingdevices, an electronic controlling device interconnected each with oneof said coupling devices, and means for applying controlling potentialsto said thermionic devices for increasing the fidelity characteristic ofthe system and decreasing the signal energy transfer through one of saidcoupling devices in response to an increased average signal amplitude,and for increasing the effective circuit coupling through another ofsaid coupling devices in response to an increased average signalamplitude, whereby.

the gain in said system may be maintained substantially unaffected bychanges in the fidelity and selectivity characteristics thereof 11. Asignal amplifying system including a plurality of cascade connectedelectronic amplifying devices and a volume control means thereforresponsive to changes in the average amplitude of an applied signal,characterized by the fact that the volume control means comprisesvariable impedance devices connected in shunt with certain of theinterstage coupling means in the amplifying system at two difierentpoints to variably load the signal channel of the system, and means forapplying controlling potentials to said variable impedance means in adirection to cause the impedance value of one of impedance means toincrease when the signal strength is increased and the gain at each ofsaid points to be controlled inversely with respect to the other.

12. The combination with an electronic signal amplifier including aplurality of electronic amplifier devices and coupling means connectingsaid devices in cascade relation to each other, of a plurality ofcontrol circuits for said amplifier, each of said circuits beingconnected with a diiierent one of said coupling means and including anelectronic control device, means for applying biasing potentials to saidcontrol devices, means for varying said potentials for two of saiddevices inversely in response to changes in the average amplitude ofsignals transmitted through said amplifier, and means responsive to saidinverse potential variations for varying the selectivity in the samesense and the gain in the opposite sense through two of said couplingmeans.

13. In a signal receiving system, the combination of means providing twotuned coupled signal circuits, an electronic control device providing avariable impedance across one of said circuits, and means for increasingthe impedance of said control device in accordance with increases in theaverage amplitude of received signals.

14. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means between at least two ofsaid devices comprising a pair of coupled tuned circuits, meansincluding the space current path of an electric discharge tube providinga variable impedance in parallel with one of said tuned circuits, andmeans for increasing the impedance of said path in response to areceived signal, thereby to vary the selectivity of said system throughsaid coupling means inversely with the impedance of said means.

15. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means between at least two ofsaid devices comprising a pair of coupled tuned circuits, meansproviding a signal controllable variable impedance in parallel with oneof said tuned circuits, and means for increasing the effective value ofsaid impedance in response to increases in the signal amplitude, therebyto vary the selectivity of said system through said coupling meansinversely with the impedance of said variable means.

16. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means between at least two ofsaid de vices comprising a pair of coupled tuned circuits, an electroniccontrol device connected in parallel with one of said tuned circuits,and means for impressing control potentials on said control device inresponse to received signals in a direction to vary the selectivity ofsaid system through said coupling means inversely with the impedance ofsaid control device.

1'7. Ina radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means between at least two ofsaid devices comprising a pair of coupled tuned circuits, an electroniccontrol device connected in parallel with one of said tuned circuits,and means for increasing the impedance of said control device inaccordance with increases in the amplitude of a signal impressed uponsaid system.

18. In a radio receiving system, the combination of a plurality ofelectronic amplifying devices, automatic volume control means therefor,means providing two tuned coupling circuits between at least two of saidelectronic devices, electronic tube means providing a variable impedanceacross one, of said tuned circuits, and means for impressing controllingpotentials from said automatic volume control means on said electronictube to cause the impedance thereof to increase with increases on signalstrength and thereby to vary inversely the selectivity and gain of thesystem through said coupling device.

19. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, automatic means for controlling the gainin said amplifier devices, coupling means between at least two of saiddevices, and manual means for varying the selectivity of said couplingmeans, said last named means including a variable impedance connected inparallel with one element of said coupling means.

20. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, automatic means for controlling the gainin said amplifier devices, coupling means between at least two of saiddevices, and means for varying the selectivity of said coupling meansincluding an electronic control device and manual means for varying theimpedance of said control device.

21. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means for said amplifier devices,signal controlled means for deriving control potentials varying inopposite sense, and means for utilizing said control potentials to varythe selectivity of at least two of said coupling means in the samesense.

22. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means for said amplifier devices,a pair of electronic control devices, means for applying controllingpotentials to said devices in opposite sense in response to varie ionsin the average signal amplitude, and means providing connections betweeneach of said control devices and one of said coupling devices to providea variable load thereon, said coupling devices including couplingelements responsive to variations in load to vary the fidelitycharacteristic of the system in the same sense in each of said couplingmeans.

23. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means for said amplifier devices,a pair of electronic control devices, means for applying controllingpotentials to said devices in opposite sense in response to variationsin the average signal amplitude, means providing a connection betweeneach of said control devices and one of said coupling devices to providea variable load thereon, said coupling devices including couplingelements responsive to variations in load to vary the fidelitycharacteristic of the system in the same sense in each of said couplingmeans, and one of said coupling means including a transformer havingtuned coupled windings across one of which said loading means isconnected, whereby the selectivity and gain through said last namedcoupling means may vary inversely with variations in loading.

24. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, automatic means for controlling the gainin said amplifier devices, means for varying the selectivity of saidsystem through said-amplifier devices including electronic means forloading differing signal conveying circuits between the amplifierdevices, means for derivingcontrolling potentials for said electronicmeans which vary in abizslzs coupled circuits, an electronic tube havingits space current path substantially in parallel with one of said tunedcircuits, automatic volume control means for said amplifier connectedwithsaid last named tube to supply controlling potentials thereto in adirection to cause the effective coupling between said circuits todecrease in response to a decrease in signal strength.

26. In a radio receiving system, the combina- 1 tion of a plurality ofelectronic amplifier devices,

automatic means for controlling the gain in said amplifier devices,coupling means between at least two of said devices, and automatic meansvarying the selectivity of said coupling means, said 20 last named meansincluding an electronic amplifier device having a control electrode andhaving its space-path connected in parallel with one element of saidcoupling means.

27. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, automatic means for controlling the gainin said amplifier devices, coupling means between at least two of saiddevices, automatic means varying the selectivity of said coupling means,said last named means including an electronic amplifier device having acontrol electrode and having its spacepath connected in parallel withone element of said coupling means, and said control electrode beingconnected with said automatic gain con- 35 trolling means to receive acontrolling potential therefrom.

28. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices,

automatic means for controlling the gain in said 40 29. In a radioreceiving system, the combination of a plurality of electronic signalamplifier devices, automatic means for controlling the gain in saidamplifier devices, coupling means between at least two of said devices,and automatic means for varying the selectivity of said coupling means,

said last named means being responsive to changes in the anode currentof at least one of said signal amplifier devices.

30. In a radio receiving system, the combinacoupling means for saidamplifier devices, signal controllable means for deriving controlpotentials varying in opposite sense, said signal controllable meansincluding an electronic amplifier device in tion of a plurality ofelectronic amplifier devices,

the signal amplifying channel of said system, and

means for utilizing said control potentials to vary the selectivity ofat least two of said coupling means in the same sense.

31. In a radio receiving system, the combina- 7 tion of a plurality ofelectronic amplifier devices, coupling meansfor said amplifier devices,signal controllable means for deriving control potentials varying inopposite sense, said signal controllable means including an electronicamplifier device and a phase-changing electronic device coupled thereto,and means for utilizing said control potentials to vary the selectivityof at least two of said coupling means in the same sense.

32. In a radio receiving system, an electronic signal amplifierincluding an amplifier tube, an automatic volume control tube, a controltube for said amplifier coupled to said automatic vol-' ume control tubeto receive controlling potentials therefrom, a second control tube forsaid amplifier coupled to said signal amplifier tube to receivecontrolling potentials therefrom, and means for coupling said controltubes to said amplifier to control the selectivity thereover in responseto variations in said controlling potentials.

33. In a radio receiving system, the combination with electronicamplifier devices and coupling means between said devices, ofcontrollable damping means for said coupling means, means for derivingcontrolling potentials proportional to the amplitude of the carrier waveof received signals, and means for simultaneously controlling the gainin said system by applying said controlling potentials simultaneously tothe electronic amplifier devices and to the controllable damping means.

34. The combination with an electric signal amplifier, of means forvariably loading a signal conveying circuit of said amplifier, meansresponsive to variations in signal amplitude for controlling the gain ofsaid amplifier, said last named means including an impedance deviceproviding a variable potential and an electronic amplifier tubeproviding a coupling means between said last named impedance and saidvariable load means.

35. In an electric signal amplifier, means providing an automaticvolume. control potential therefor, means for reversing the phase ofvariations in said potential, variable loading means for a signalconveying circuit of said amplifier, said last named means beingresponsive to variations in a controlling potential, said loading meansbeing connected to said phase reversing means to receive a controllingpotential therefrom.

36. In an electric signal amplifier, the combination with a signalconveying circuit and an electronic amplifier, of means for deriving anautomatic volume control potential for said amplifier, variable loadingmeans for said circuit, and means including an electronic amplifier tubefor reversing the phase of variations in said automatic volume controlpotential and for applying said reversed potential to said loading meansto control the same.

3'7. In a signal amplifier, the combination with a pair of electronicamplifier devices and signal coupling means interconnecting said device,of 5 meansproviding variable electrical damping for said coupling meansresponsive to potential variations, automatic volume control meansproviding a signal variable potential, and means for utilizing saidpotential to simultaneously control the gain in at least one of saidamplifier clevices and the damping of said coupling means.

38. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means for said amplifier devices,automatic volume control means for deriving control potentialproportional to the amplitude of the carrier wave of. received signals,and means for utilizing said control potential to control simultaneouslythe signal gain in said system and damping of circuits connected withsaid coupling means.

39. In an electronic signal amplifier, the combination with a pluralityof cascade connected electronic amplifier devices, of means forsimultaneously changing an operating characteristic of certain of saidelectronic amplifier devices and the coupling between said devices, saidmeans being responsive to variations in a controlling potential, signalresponsive amplifier device for deriving potentials which vary inopposite sense in response to signal variations, and means for applyingsaid potentials to said amplifier devices and to said coupling means.

40. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means for said amplifier devices,signal controllable means including separate electronic amplifierdevices for deriving control potentials varying in opposite sense, andmeans for utilizing said control potentials to vary the selectivity ofat least two of said coupling means in the same sense.

41. In a radio receiving system, the combination of a plurality ofelectronic amplifier devices, coupling means for said amplifier devices,signal controlled means for deriving control potentials varying inopposite sense, means for utilizing said control potentials to vary theselectivity of at least two of said coupling means in the same sense,and means providing a common source of operating potentials for the gridand anode circuits of said amplifier devices and selectivity controllingmeans.

GEORGE L. BEERS.

